Adding checkbox overlay for addon
You would prolly have to edit the overlays file to get it in that location. Pretty easy to add settings to overlays though.



import bpy

def draw_stats_overlay(self, context):
    layout = self.layout
    win = context.window_manager

    layout.label(text="Show Stats")
    layout.prop(win, 'stats_toggle')


def register():
    bpy.types.VIEW3D_PT_overlay.append(draw_stats_overlay)

    bpy.types.WindowManager.stats_toggle = bpy.props.BoolProperty(
        name = "Toggle Stats",
        default = False
      )

def unregister():
    bpy.types.VIEW3D_PT_overlay.remove(draw_stats_overlay)
    del bpy.types.WindowManager.stats_toggle

if __name__ == "__main__":
    register()




Edit:

You might could do something like this.

Remove just the guides settings.

import bpy


bpy.utils.unregister_class(bpy.types.VIEW3D_PT_overlay_guides)




Add the settings back with the new setting.

import bpy

def guides_with_new_settings(self, context):
    layout = self.layout

    view = context.space_data
    scene = context.scene

    overlay = view.overlay
    shading = view.shading
    display_all = overlay.show_overlays

    col = layout.column()
    col.label(text="Guides")

    col = layout.column()
    col.active = display_all

    split = col.split()
    sub = split.column()

    row = sub.row()
    row_el = row.column()
    row_el.prop(overlay, "show_ortho_grid", text="Grid")
    grid_active = (
        view.region_quadviews or
        (view.region_3d.is_orthographic_side_view and not view.region_3d.is_perspective)
    )
    row_el.active = grid_active
    row.prop(overlay, "show_floor", text="Floor")

    if overlay.show_floor or overlay.show_ortho_grid:
        sub = col.row(align=True)
        sub.active = (
            (overlay.show_floor and not view.region_3d.is_orthographic_side_view) or
            (overlay.show_ortho_grid and grid_active)
        )
        sub.prop(overlay, "grid_scale", text="Scale")
        sub = sub.row(align=True)
        sub.active = scene.unit_settings.system == 'NONE'
        sub.prop(overlay, "grid_subdivisions", text="Subdivisions")

    sub = split.column()
    row = sub.row()
    row.label(text="Axes")

    subrow = row.row(align=True)
    subrow.prop(overlay, "show_axis_x", text="X", toggle=True)
    subrow.prop(overlay, "show_axis_y", text="Y", toggle=True)
    subrow.prop(overlay, "show_axis_z", text="Z", toggle=True)

    split = col.split()
    sub = split.column()
    sub.prop(overlay, "show_text", text="Text Info")
    sub = split.column()
    sub.prop(overlay, "show_cursor", text="3D Cursor")

    if shading.type == 'MATERIAL':
        col.prop(overlay, "show_look_dev")

    split = col.split()
    sub = split.column()
    sub.prop(overlay, "show_annotation", text="Annotations")

    #Add my new setting here
    sub = split.column()        
    sub.prop(context.window_manager, "stats_toggle", text="Toggle Stats")


def register():
    bpy.types.VIEW3D_PT_overlay.append(guides_with_new_settings)

    bpy.types.WindowManager.stats_toggle = bpy.props.BoolProperty(
        name = "Toggle Stats",
        default = False
      )

def unregister():
    bpy.types.VIEW3D_PT_overlay.remove(guides_with_new_settings)
    del bpy.types.WindowManager.stats_toggle


if __name__ == "__main__":
    register()




Addon example

bl_info = {
    "name": "Overlay Stats Test",
    "version": (0, 0, 2),
    "blender": (2, 82, 0),
    "location": "",
    "description": "",
    "warning": "",
    "wiki_url": "",
    "category": "3D View",
}

import bpy


#Guide settings with new setting added
def guides_with_new_settings(self, context):
    layout = self.layout

    view = context.space_data
    scene = context.scene

    overlay = view.overlay
    shading = view.shading
    display_all = overlay.show_overlays

    col = layout.column()
    col.label(text="Guides")

    col = layout.column()
    col.active = display_all

    split = col.split()
    sub = split.column()

    row = sub.row()
    row_el = row.column()
    row_el.prop(overlay, "show_ortho_grid", text="Grid")
    grid_active = (
        view.region_quadviews or
        (view.region_3d.is_orthographic_side_view and not view.region_3d.is_perspective)
    )
    row_el.active = grid_active
    row.prop(overlay, "show_floor", text="Floor")

    if overlay.show_floor or overlay.show_ortho_grid:
        sub = col.row(align=True)
        sub.active = (
            (overlay.show_floor and not view.region_3d.is_orthographic_side_view) or
            (overlay.show_ortho_grid and grid_active)
        )
        sub.prop(overlay, "grid_scale", text="Scale")
        sub = sub.row(align=True)
        sub.active = scene.unit_settings.system == 'NONE'
        sub.prop(overlay, "grid_subdivisions", text="Subdivisions")

    sub = split.column()
    row = sub.row()
    row.label(text="Axes")

    subrow = row.row(align=True)
    subrow.prop(overlay, "show_axis_x", text="X", toggle=True)
    subrow.prop(overlay, "show_axis_y", text="Y", toggle=True)
    subrow.prop(overlay, "show_axis_z", text="Z", toggle=True)

    split = col.split()
    sub = split.column()
    sub.prop(overlay, "show_text", text="Text Info")
    sub = split.column()
    sub.prop(overlay, "show_cursor", text="3D Cursor")

    if shading.type == 'MATERIAL':
        col.prop(overlay, "show_look_dev")


    split = col.split()
    sub = split.column()
    sub.prop(overlay, "show_annotation", text="Annotations")

    #Add my new setting here
    sub = split.column()        
    sub.prop(context.window_manager, "stats_toggle", text="Toggle Stats")


#Guide settings without new setting
def guides_without_new_settings(self, context):
    layout = self.layout

    view = context.space_data
    scene = context.scene

    overlay = view.overlay
    shading = view.shading
    display_all = overlay.show_overlays

    col = layout.column()
    col.label(text="Guides")

    col = layout.column()
    col.active = display_all

    split = col.split()
    sub = split.column()

    row = sub.row()
    row_el = row.column()
    row_el.prop(overlay, "show_ortho_grid", text="Grid")
    grid_active = (
        view.region_quadviews or
        (view.region_3d.is_orthographic_side_view and not view.region_3d.is_perspective)
    )
    row_el.active = grid_active
    row.prop(overlay, "show_floor", text="Floor")

    if overlay.show_floor or overlay.show_ortho_grid:
        sub = col.row(align=True)
        sub.active = (
            (overlay.show_floor and not view.region_3d.is_orthographic_side_view) or
            (overlay.show_ortho_grid and grid_active)
        )
        sub.prop(overlay, "grid_scale", text="Scale")
        sub = sub.row(align=True)
        sub.active = scene.unit_settings.system == 'NONE'
        sub.prop(overlay, "grid_subdivisions", text="Subdivisions")

    sub = split.column()
    row = sub.row()
    row.label(text="Axes")

    subrow = row.row(align=True)
    subrow.prop(overlay, "show_axis_x", text="X", toggle=True)
    subrow.prop(overlay, "show_axis_y", text="Y", toggle=True)
    subrow.prop(overlay, "show_axis_z", text="Z", toggle=True)

    split = col.split()
    sub = split.column()
    sub.prop(overlay, "show_text", text="Text Info")
    sub = split.column()
    sub.prop(overlay, "show_cursor", text="3D Cursor")

    if shading.type == 'MATERIAL':
        col.prop(overlay, "show_look_dev")

    split = col.split()
    sub = split.column()
    sub.prop(overlay, "show_annotation", text="Annotations")


def register():
    #Check to make sure overlay guides panel is registered
    if hasattr(bpy.types, 'VIEW3D_PT_overlay_guides'):
        #Unregister if overlay guides is registered        
        bpy.utils.unregister_class(bpy.types.VIEW3D_PT_overlay_guides)

    #Append guide settings with new setting when addon is registered    
    bpy.types.VIEW3D_PT_overlay.append(guides_with_new_settings)

    #Remove guide settings without new setting when addon is registered    
    bpy.types.VIEW3D_PT_overlay.remove(guides_without_new_settings)

    bpy.types.WindowManager.stats_toggle = bpy.props.BoolProperty(
        name = "Toggle Stats",
        default = False
      )

def unregister():
    #Remove guide settings with new setting when unregistering addon        
    bpy.types.VIEW3D_PT_overlay.remove(guides_with_new_settings)

    #Append guide settings without new setting when unregistering addon   
    bpy.types.VIEW3D_PT_overlay.append(guides_without_new_settings)

    del bpy.types.WindowManager.stats_toggle


if __name__ == "__main__":
    register()
```